Fiber reinforced polmer composite structures contain successive layers of fiber and polymer resin. During fabrication of a composite, a wrinkle in one ply of fiber material can propagate through adjoining layers to the surface, resulting in a localized region of thick resin, or a “resin pocket”. It is useful to measure the resin pocket dimensions as a means of quantifying surface wrinkle which can potentially impact the performance of a structure. Current ultrasonic non-destructive testing (NDT) methods cannot reliably detect resin pockets less than about 0.070 to 0.080 inches (70 to 80 mils) deep. Such measurements have poor accuracy and require close contact with the part. Visual inspection for resin pockets in carbon fiber reinforced plastic (CFRP) composite structures is especially difficult, due to the poor reflectivity of black carbon fibers. A non-destructive technique is needed to determine resin pocket dimensions greater than 0.0150 inches (15 mils) deep in composite structures. Such information can then be used to identify wrinkles as an indication of quality of the structure.